This invention relates to an electronic level and, more particularly, to such a level which provides a more sensitive and, thus, more accurate, representation of the orientation thereof relative to a reference plane. Preferably, the electronic level provides a representation of the relative horizontal orientation thereof and also a representation of the relative vertical orientation thereof.
Levels have long been used to provide craftsmen and artisans with indications of the relative alignment of a workpiece with respect to a horizontal or vertical plane. Such levels are used widely in the fields of construction, carpentry, etc. in which a workpiece, beam, plane, etc. must be aligned with the horizontal or vertical.
Typically, levels have been formed generally as elongated members having two (or more) containers partially filled with liquid so as to form a permanent bubble in each container. One container is predisposed such that the bubble, although free to move from end thereof to the other, nevertheless is centrally located within the container when the level (and, thus, the liquid within this container) exhibits proper horizontal alignment. Similarly, the other container is predisposed such that, when the level is used to indicate vertical alignment, the bubble in this container likewise is positioned in the center of the container. Suitable reference marks normally are provided on the respective containers such that the user can ascertain easily when the respective bubbles are centrally positioned.
While such mechanical levels have been used successfully for several years, it had been thought that more accurate indications and more easily observable displays could be derived by adapting electronic circuitry to such instruments. One example of an electronic level is described in U.S. Pat. No. 4,079,521, in which two capsules containing mercury globules are used to indicate the relative deviation of the level from, for example, the horizontal plane. The housing in which these mercury switches are contained may be rotated when the level is used to indicate vertical alignment. One drawback of the electronic level described in this patent is that the mercury switches provide only a small number (e.g. three) of indications of alignment. This is due to the fact that the mercury-filled capsules function as simple on/off switches and do not permit a more continuous spectrum of alignment indications. That is, the mercury-filled capsules function as discrete sensors which may indicate, for example, "up", "down" or "level" alignments.
A modification of the electronic level described in the aforementioned patent is set out in U.S. Pat. No. 4,152,839. Here, a mercury globule slides in a capsule between two opposite end electrodes, the mercury completing a circuit to one or the other of these electrodes when the level is tilted upward or downward, respectively. Corresponding indications are provided as a display of the orientation of the level. When the level is horizontal, the mercury globule completes a circuit to a center electrode, resulting in a corresponding visual display. In this patent, two separate capsules are provided, one for sensing and indicating horizontal alignment of the level and the other for sensing and indicating vertical alignment thereof. Here too, however, only discrete indications are sensed and displayed: up, down or level. The user is not apprised of an approaching level condition and, thus, he may find it time-consuming and even difficult to detect proper horizontal (or vertical) orientation.
U.S. Pat. No. 2,910,782 relies upon a pool of mercury which extends across a number of contacts depending upon the horizontal orientation, or tilt, of its container. Thus, depending upon the degree of tilt, a corresponding number of contacts engage the mercury, resulting in the lighting of one or more lamps. A similar level-indicating device is described in U.S. Pat. No. 1,375,278.
Various other leveling instruments have been suggested in the past, such as those which rely upon reflection and refraction of light beams as a representation of the horizontal (or vertical) orientation of the device.
A common deficiency found in the electronic level instruments described in the aforementioned patents is the sensing thereof of discrete orientations of the level itself. That is, an upward or downward tilting is sensed by the particular electrical contacts, or electrodes, which are engaged by a moving globule of mercury. This results in a somewhat less than accurate instrument. The orientation of the level between, for example, two discrete positions cannot be sensed.
Another disadvantage associated with the aforementioned electronic levels is the requirement for the user to operate a manual switch when the level is changed from a generally horizontal orientation to a vertical orientation. If the switch is not suitably operated, for example, if the user forgets to actuate it, the level will not operate in its new orientation.
Yet another disadvantage of these devices is the omission therein of a power conservation device. As a result, if the level is not used, the failure to open the power switch will result in a rapid drain of the batteries used therewith.